Photographic timing device



Allg- 23, 1960 l.. L. wElsGLAss 2,949,811

PHOTOGRAPHIC TIMING DEVICE Filed Feb. 17, 1956 3 Sheets-Sheet 1 TWL EXPSl//E WMF /A/ 5650/3/55 INVENTOR.

0l/l5 L. VE/56.4 155 Aug. 23, 1960 l.. L. wElsGLAss PHOTOGRAPHIC TIMING DEVICE:

Filed Feb. 17. 195s 3 Sheets-Sheet 2 Aug- 23, 1950 L. L. wEisGLAss 2,949,811

PHOTOGRAPHIC TIMING DEVICE Filed Feb. 17, 1956 3 Sheets-Sheet 3 Iig-r FX U B077/ lf 60% Cam INVENTOR. 0d/5 ,L VE/550955.

United States Patent C) 2,949,811 PHOTOGRAPHIC 'rlMlNG DEVICE Louis L. Weisglass, New York, N.Y., assignor to Simon Brothers, Inc., Long Island City, N.Y., a corporation of New York Filed Feb. 17, 1956, Ser. No. 566,180 Claims. (Cl. 88-24) The present invention relates to timing devices and more particularly to a timing device or time computing apparatus which may be preset to accurately and precisely cause automatic sequential operation of other apparatus at the desired instant and for a partial preselected period of time out of a total predetermined period of operation of the Vtiming device wherein the ratio of total predetermined period of time to partial preselected period of time, will remain constant once selected and set, regardless of change in the total period of time. In other words, the timing device of the present invention is iirst preset for any one of a range of total time periods of operation and secondly preset so that during such total period at precise instants the timing device operates to cause the operation of other apparatus for preselected portions of the total time period for which such timing device is preset. The timing device will also permit changes in total time without alteration in the percentage relationship between the lrst and second operation.

Timing devices of a somewhat similar nature are known to the prior art in which fractional periods of a total time can be selected which are theoretically proportional and hence have a certain ratio to each other but such prior art devices are known to be unreliable. This is because of the Very fact that they are based on this theoretical ratio and hence necessarily vary widely at different time settings. While this may not be too serious under certain timing conditions, there are more and more situations developing every day, such as in connection with guided missiles, the mixing of chemical compounds, and in connection with photographic eX- posures, where such inaccuracies cannot be tolerated and hence these prior art timing devices are useless for these latter purposes. Timing devices of the prior art are also inconvenient to operate since in most cases it is necessary to readjust the proportional time setting whenever the total time setting is changed for any reason. This is obviously inconvenient if one wishes, for example, to provide for the mixing of chemicals where the timer controls the flow of a liquid chemical and it is then desired to introduce a second liquid chemical at the appropriate time to yield a mixture of the proper proportion. If in this case one wishes to change the quantity of the total mixture without altering the proportion between the two components, it would be necessary to readjust the control that introduces the second component, in which case these prior art devices would be inconvenient for this purpose.

It is `accordingly the primary object of the present invention to provide a timing device which is very accurate in its operation, regardless of its total time setting, for any preselected fractional part of its total preset time of operation, and in which the total preset time may be varied independently of this fractional preset time of operation, or vice versa.

Another object of the present invention is the provision of ian accurately operable timing device which may be preset for any desired total time period of operation and also preset to select any desired fractional part of such total time period with this fractional period being very precise and accurate for any and all settings with respect to the total time period.

A further object of the present invention is the provision of an exceedingly accurate timing device which controls a supply of electrical energy for a given period of time and also simultaneously controls a second supply of electrical energy for a desired preselected proportion of the time as selected for the total time of the first supply of energy.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawings wherein:

Figure l is a plan elevation partly in cross-section of the timing device of the present invention;

Fig. 2 is a sectional View taken on the line II1I of Fig. l and looking in the direction indicated by the arrows;

Fig. 3 is a graphic illustration wherein the abscissa represents potentiometer resistance corresponding to total exposure time in seconds and the ordinate grid voltage on the thyratron control tube as well as such grid voltage minus lixed grid bias voltage, and which tube forms part of the time control circuit with which the timing device or time computer of the present invention is used;

Fig. 4 is a circuit diagram showing the electrical circuit of the timing device of the present invention as used in connection with photographic reproducing apparatus;

Fig. 5 is a schematic diagram constituting a part of the electrical circuit of Fig. 4 but showing in more detail the relationship of the two timing device potentiometers constituting the potentiometer network.

Fig. 6 is a sectional View taken along the plane of line VI-VI of Fig. 8 showing the electro-magnetically controlled color filter placed for contrast control purposes in the path of the light emanating from the enlarger of Fig. 8 and with its solenoid in a deenergized position;

Fig. 7 is a sectional view identical to that of Fig. 6 except that it shows the solenoid in an energized position;

Fig. 8 is an elevational view of a typical photographic enlarger with which the timing device of the present invention is used;

Fig. 9 is a front elevational view of the timing device or time computer of the present invention and showing the dial controls and switches;

Fig. l() is a time chart showing typical proportionate times for positioning of the lilters of Figs. 6 and 7 in the path of light from the enlarger of Fig. 8;

Fig. ll is :a fragmentary elevational View partly in cross-section of a modiiication which the enlarger of Fig. 8 may take and showing how the filters, as illustrated in Figs. 6 and 7, are operated in this modification of Fig. 1l;

Fig. l2 is a side elevational view of the modification of Fig. 11 with part of the device broken away to better illustrate the same.

Referring now to the drawings more in detail, the timing device 5 of the present invention is shown in Fig. 8 as comprising a lfront panel 6 supported from any suitable base, so that the device may conveniently rest upon a table or the like 7. A one rpm. synchronous motor S (iFig. l) having a shaft 9 is mounted by a bracket or the like 10 rearwardly of the front panel 6 and fitting over the shaft 9 is an electrically insulating bushing 12. A metallic hub 13 is in turn secured to this insulating bushing y12 carrying at one end a laterally extending metallic arm 14 and at its other end `a metallic contact arm i5 on variable contrast enlarging paper.

extending' laterally therefrom at 180 relative to the metallic arm 14, so that upon rotation of the synchronous motor 8, the insulating bushing 12, together with the hub 13 and laterally extending arms 14 and 15 also rotate as a unit about the axis ofthe motor shaft 9.

Aspiral spring 16 has one of its ends secured to` the hub 13 while the other end is secured to a post 17 forming part of the bracket 10, with the result that the normal position of the arms 14 and 15, when not rotated by the motor 8, is that as shown in Figs. l and 2, and upon cessation of rotation of motor 8 this spring 16 automatically rotates the hub in a clockwise direction (as Viewed from Fig. l), to return the arms 14 and 15 to their normal rest position as shown in Figs. 1 and 2. This spring 16, as hereinafter pointed out more in detail, likewise acts as an electrical connection to conduct electrical energy to the contact arm.

It will also be noted that a short shaft 18 passes through the panel 6 in axial alignment with motor shaft 9 and carries on its outer end a setting knob 19 having ya pointer 20 registering with a circular scale 22 (Fig.q9) on the panel 6 graduated in terms of Exposure Time.

The inner end of shaft 18 has aiiixed thereto a metallic hub 23 carrying an insulating disc 24 having a resistance winding `about its periphery to form a toroidal potentiometer 25. -A pin 26 passes through the insulating disc 24 which acts as a stop against which the contact arm 15 rests in its normal position when not rotated by the motor 8, as can be readily seen from iFigs. 1 and 2. A iixed contact arm 27 is insulatingly supported rearwardly of the panel 6 and its inherently yspring-tensioned end engages the windings of the potentiometer 25.

A switch 28 is supported rearwardly of the panel 6, such as by the bracket 10, which switch has la circuit closing button 29, depressible from the top of the timing device and a circuit opening button 30, depressible by contact arm 14 when rotated by motor 8 into contact therewith. Depression of button 29 closes a circuit, as hereinafter pointed out, to start rotation of motor 8 'While depression of button 30 by contact arm 14 opens the motor circuit to stop rotation thereof, whereupon the spring 16 returns the contact arm 15 intoV engagement with the stop pin 26 and the arm 14 simultaneouslydisengages the button 30 and moves with arm 15 until it likewise cornes to rest 180 from arm 14 and stop pin 26. As hereinbefore mentioned, the timer of the present invention may be readily used in connection with photographic exposures and particularly in the making of prints At the present tlmethere is available on the market a sensitized paper `having two layers of photographic emulsion, one of which 1s sens1t1ve to green light and yielding soft prints and the other layer responsive to blue light and producing contrasty prints. 1t has been customary in making prints with this type of paper to use a set of filters (about to a set) but this is inconvenient and time consuming since the iilters must be manually changed in order to vary the contrast and also restricted to a limited number of contrast steps.

I have found that by the use of the two extreme iilters which transmit only the green and blue light, respectively, and by accurately timing the exposure with each of these lt'ers, a very satisfactory photographic print with iniinlte attenuation of contrast (within range of paper) Vcan be conveniently and automatically obtained on variable contrast paper. This may be appreciated by reference now more especially to Fig. 8 which shows a wellknown type of photographic enlarger comprising a baseboard 32 having a bracket 33 secured thereto and which supports upright channels 34 forming slides for the projector carriage 35. Rollers 36 facilitate movement of the carriage longitudinally of the channels 34 with the weight of the carriage 35 being counterbalanced by a spring 37.

The projector proper comprises a housing for a lamp plate 48 by a link 56. t .the green transmitting lter 50 in lalignment wlth the light 38 and a double condenser 39, with a holder 40 for the photographic negative immediately below the condenser. A lens 42 projects an enlarged image of the negative on to the sensitized paper 43 resting on the baseboard 32. This lens `42 is mounted on a carrier 44 which is vertically adjustable by means of a friction drive 45 until the operator obtains the desired sharp focus, and the lens is connected to the iilm holder 40 by a flexible light-tight bel* lows 46. Thus the enlarger as illustrated in Fig. 8, is of well known construction and needs no further detailed description, other than to point out that the lens carrier 44 supports a color filter assembly 47, shown more in detail in Figs. 6 `and 7.

By reference to these latter iigures it will be obvious that such assembly comprises a pivoted plate 48 supporting a blue transmitting filter 49 and a green transmitting iilter 50, although other color transmitting iilters may be utilized depending upon the particular variable contrast emulsion used with the paper. The plate 48 rotates labout a pivot 52 secured to a base 53 which in turn is lfastened to the lens carrier 44.v `Carried by this base 53 is a solenoid 54, having its armature 55 connected to the A coil spring 57 normally holds emanating from the projector assembly in the deenergized position of the solenoid 54, as shown in Fig. 6, and which spring is further tensioned, upon energization of the solenoid to position the blue transmitting iilter 49 in alignment with the light beam, as seen in lFig. 7.

The timing device 5, as shown in Figs. l, 2 and 9, is connected to the filter assembly 47 by an electrical arrangement shown more in detail in Fig. 4. As illustrated in this latter iigure, as Well as Fig. 9, the timing device 5, in addition to being provided with the 5000 ohm motor-driven toroidal potentiometer 25, is also provided with a second potentiometer 60 of about 50,000 ohms which is adjusted by a knob 62 on the front of the panel 6 and having a pointer 63 registering with graduations 64 circularly disposed on the front of the panel 6 repre-1 senting percentage of Contrast in terms of blue light. An additional linear potentiometer 65 of about 10,000 ohms isalso provided rearwardly of the panel 6 which, once adjusted for given conditions, need not be further disturbed during normal operation of the timing device, as hereinafter mentioned more in detail.

Also carried by the timing device 5 is a transformer ,66, the primary winding 67 of which is connected to a Power Supply by closure of a switch 68 operable from the front of panel 6 and a pilot light 69, when lighted condenser 74 includes the indirectly-heated cathode 72 and grid 76 of the thyratron tube 73 so that a negative biasing voltage is normally applied to this grid 76 to make the thyratron tube non-conducting, as hereinafter set forth more in detail. lThe plate circuit of this tube 73 extends from one side of the Power Supply through a conductor 77 to the cathode 72 and from the anode or plate 78 through a conductor 79 to the winding of solenoid 54 and thence by means of a conductor 80 to the other side of the Power Supply, so that when the thyratron tube 73 is rendered conductive the solenoid 54 is energized,

-thus moving the green transmitting filter 50v out of the light beam from the lamp 38 and inserting the blue translmitting filter 49 in its place, as previously mentioned. A `resistor 82 of about 750 ohms is shunted across the windfor iighting the lamp 38 for focusing or printing as selected, and such conductor 80 also connects to one point of the microswitch 28 to complete a circuit to the synchronous motor 8 (and the lamp 38 depending upon the position of switch 83) when the microswitch button 29 is depressed because a further conductor 84 completes a circuit to the other side of the power supply from both the motor 8 and the lamp 38. vFor the purpose of providing a grid control voltage for the thyratron tube 73, a secondary winding 85 is provided on the transformer 66 which supplies an A.C. voltage of about 120 volts 180 out of phase with -respect to the 117 volt Power Supply for the plate circuit of the tube 73. From Fig. 4 it will be noted that one end of this secondary winding 85 is connected by a conductor 86 to one end of the winding of Timing potentiometer 25 while the other end of this secondary winding 85 is connected by a conductor 87 to the remaining end of the winding of Timing potentiometer 25 as well well as such conductor 87 being also connected to one end of the winding of Contrast potentiometer 60. The remaining end of the winding of Contrast potentiometer 60 is connected to the contact arm 27 of Timing potentiometer 25 by a conductor 88 while the movable contact 89 of Contrast potentiometer 60 is connected by a conductor 90 to the sliding contact arm 92 of potentiometer 65 and to complete the grid biasing circuit for the thyratron tube 73, the movable contact arm 15 of Timing potentiometer 25 is connected by the spiral spring 16 and a conductor 93 to the screen grid 94 and indirectly heated cathode 72 of thyratron tube 73.

From the foregoing itshould be obvious that the total exposure time required to print a picture on the sensitized paper 43 is the sum of the time periods that each of the green and blue transmitting filters are positioned in the light beam emanating from the lamp 38, and it is the proportion of green time to blue time which is a measure of the contrast so that if one utilizes 100% blue throughout the total exposure time that yields 100% contrast, then 100% green throughout the exposure will yield v% contrast. In order to obtain the best prints having the best desired contrast the timing device of the present invention accordingly produces the proper preselected time periods by moving one of the filters out of. the light beam and the other filter into the light beam for a preset partial period of the total exposure time. Moreover, regardless of the required total exposure time the partial time selected will always be an accurate fraction of any and all total exposure times, and will remain the same fraction thereof, if so desired, regardless of change in total exposure time. This is accomplished by lthe utilization of the double-armed Timing potentiometer 25 and the single-armed Contrast potentiometer 60, forming an electrical computing network.

This may be better appreciated by specific reference to Fig. 5 from which it will be noted that the Fixed Bias Supply, comprising the adjustable resistance 65 and Vcondenser 74 (Fig. 4), when once set by the arm 92 for a negative potential of just below -1.5 volts, which is the critical breakdown voltage of thyratron tube 73, need not be further disturbed, and this voltage of just below -1.5 volts is impressed across the indirectly heated cathode 72 .and the grid 76 wh'ich in the absence of any other voltage renders the thyratron tube 73 non-conducting. The potentiometers 25 and 60 are both linear and hence the voltages thereacross, as hereinafter described more in detail, are proportional to resistance or voltage, or time. Accordingly, in order to set the total exposure time the knob 19 is rotated until its pointer registers with the proper graduation 22 4on the dial which, as shown in Fig. 9, is selected at 35 seconds. Rotation of such knob 19 rotates the toroidal potentiometer 25 which carries ywith it the pin 26 thus causing the contact arm 15 which abuts on pin 26 to rotate the hub 13. Rotation of the hub 13 will of course cause rotation of shaft 9 and arm 14. It can be seen that contact arm 15 will remain in abutment and follow pin 26 at any time setting, by the action of spring 16 so long as motor 8 does not cause rotation of shaft 9. When rotation of the exposure timing knob 19 is discontinued by the operator, the stationary contact arm 27 will be in engagement with a different point on the winding of toroidal potentiometer 25.

Comparing the setting of Timing potentiometer 25 by rotation of knob 19 with the schematic showing of Fig. 5, this is equivalent to moving the contact 27 to the position on the potentiometer 25 where the resistance of the latter is such that a voltage a will exist across that portion of the potentiometer 25 remaining in the control circuit and which voltage will be of lower or equal value than the voltage b across the entire potentiometer 25 which is the 120 volts supplied by the conductors 86 and 87 or voltage E. Next the operator sets the Contrast control knob 62 by rotating it until its pointer 63 registers with the desired graduation 64 on the front of panel 6 which in this instance, as shown in Fig. 9, is 60 which thus means that the green transmitting filter 50 has been selected to remain in the path of the light beam from lamp 38 for 40% of the total time of thirty-tive seconds (which is 14 seconds) after which the blue transmitting filter 49 will be substituted therefor for the remainder of the total time of thirty-tive seconds (which is 2l seconds) as shotwn more clearly by the dotted line in Fig. 10. Referring again to Fig. 5 the setting of the contrast knob 62 is equivalent to moving the contact arm 89 along Contrast potentiometer 60 to the point, as shown in Fig. V5, where the resistance is such that4 a Vvoltage c exists thereacross which is of equal or lesser value than the Voltage d acrossthe entire resistance of Contrast potentiometer 60.

At these :above arbitrarily selected settings of the control knobs 19 and 62, it can be seen that the following condition exists: The impressed votlage of v. across potentiometer 25, as can be seen in Fig. 3, represents a total exposure time of 60 seconds because of the fact that arm 15 is driven by a one r.p.rn. motor. Therefore, when arm 27 is set (movement relative to potentiometer 25) for a total exposure time of 35 seconds, voltage a will be:

3%0X120=7O volts Since voltage d equals voltage ya, voltage c will be:

and will be impressed on the grid 76 of thyratron tube 73, as can be seen by reference to Fig. 3, before starting of the timing device 5 which is at zero time. Also at this zero time the rotatable Contact arm 15 will be held by the spring 16 against pin 26 at the end of the IWinding of Timing potentiometer 25 which in effect is the same -as being connected to the supply conductor 87, as shown in the circuit diagram of Fig. 4. However, upon movement of contact arm 15 along the windings of potentiometer 25, a voltage f of increasing value is developed between the movable arm 15 and the end of the potentiometer to which conductor 87 is` connected, as shown in Fig. 5.

Having now set the control knobs 19 and 62 to the desired exposure time and contrast, the operator then closes the power switch 68 thus lighting signal lamp 69 and energizing transformer 66. Switch 83 is then moved to its Focus position which energizes lamp 38 and the projector carrier is then moved longitudinally of its channels 34 to obtain the desired sharp focus at the baseboard 32 prior to positioning the sensitized paper thereon. After accomplishing the proper focus setting switch 83 is then moved to its Print position Iwhich extingushes lamp 38 Iand after placing the sensitized 7 paper 43 on the baseboard 32, the timing device is then ready for operation.

The operator then depresses push-button 29 which closes the contacts of rnicroswitch 28 and completes a circuit to the constant-speed synchronous motor 8 by a circuit extending from'the Power Supply through conductor 80 to a terminal of the mcroswitch' 28 thence through this switch to motor 8 and back to the Power Supply through conductor 84, thus energizing vmotor 8. At the same instant that the lmotor 8 is' energized lamp 38 is also again energized byclosure of microswitch 28 as -can be seen from Fig. 4. Energization of motor 8 causes it to rotate the hub 13 which carries with it the arms 14 and 15 with the latter leaving the pin 26 and moving around the toroidal winding of potentiometer25. The entire travel (in terms of length as viewed from Fig. and in terms of rotation las viewed from Figs. 1, 2 and 4) of contact arm 15 from its position of rest against the pin 26, is determined by the total arcuate rotation of the arm 14 from its axial position, as set by rotation of knob 19 (for 35 seconds in the example), until it contacts the push-button 30 of the microswitch 28, to again open the switch and deenergize the motor 8 and lamp 38 (which thus constitutes the total exposure time) at which instant the tensioned spiral spring 16 will automatically return the Contact arm to its normal rest-position against the pin 26.

During the travel of contact arm 15 at the constant speed of motor 8, a voltage variation occurs between arms 15 and 89 which follows a straight line such as shown in Fig. 3.

For example, with the Contrast set at 60% as shown in Figs. 4, 5 and 9 (which indicates the percentage of the total exposure time that the blue ilter is in light beam) during the total exposure time of thirty-tive seconds, the voltage Er (Fig. 5) from the potentiometer network will vary, due to rotation of the contact arm 15, (from its initial -28 volts until it reaches zero volts which variation occurs at a point that will permit the blue transmitting filter to be in the light beam for 60% of the total exposure time, or after 40% of the total exposure time has elapsed (Le. 14 seconds) as shown in Figs. 3 and 10, and where the voltage f equals +28 volts. That is to say, when the voltage Er (Fig. 5) of the potentiometer network thus reaches zero, the only control voltage on the grid is the 1.5 volts from the iixed bias supply (Fig. 5), and since this is the critical breakdown voltage `of the thyi'atron tube 73, it immediately becomes conductive :and energizes the solenoid 54, accompanied by substitution of the blue transmitting filter 49 for the green transmitting filter 50. Such substitution of lters will continue for the remaining 60% of the total time period, or twenty-one seconds, because the continued rotation of the potentiometer contact arm 15 merely changes the potentiometer network voltage to an increasingly higher positive value (180 out of phase), as shown by the graph line of Fig. 3, until the arm 14 engages` the push button 30 at the expiration of the total exposure time, thus deenergizing the motor 8 with return of contact arm 15 lto its normal starting position against the pin 26, as above mentioned.

The fact that throughout the range of total exposure times any `selected proportion of such time, as a measure of contrast, remains accurately the same may be better understood by the lfollowing mathematical formula computed in accordance with the voltages shown more specifically in Fig. 5. For example, as above noted the contact arm 15 is continuously changed in position at a constant rate from the starting point ofV potentiometer 25 to some preselected position by rotation of the constant-speed one r.p.m. synchronous motor 8, while arm 27 of Timing potentiometer 25 was manually preset to a desired total time and the arm 89 of Contrast potentiometer 60 lwas likewise manually preset to a-desired percent of contrast which in effect is a definite i8 perecentagetime of the -totalpreset exposure time.'v LSince the two potentiometers 25 and 60, as Vhereinbefore noted, are linear, the resistance value across such potentiometers designated f, a, b, c and d in Fig. 5, are proportional and are thus proportionalA to voltage thereacross as well fas to time. f lf, therefore, A, l j

Ts is the total or preset exposure time, andv -Tp is the percentage time (contrast in terms of blue) then Trz T. a

d is representative of the percentage, then EL d a,

The voltage across y I: I fr Ef Eb The voltage across a c C E Era Assuming Err-0, then Ef=Ec Therefore,

l... 2.2 Eb Eb d i d a It is thus apparent from the above mathematical yderivation that the time TS is adjusted by changing the posi'- tion of arm 27 (but since this is stationary it isfaccornplished by rotating the toroidal potentiometer 25) as hereinbefore pointed out, and that simil-arly the percentage time (or contrast) Tp is adjusted by changing the position of arm 89 in relation to the potentiometer 460. Moreover, regardless of the total time setting 'FS, the `percentage time or contrast Tp` will remain accurately .the same proportion of the .total time. This can be also appreciated from the showing ofthe dotted lineV in Fig. 10. In this instance a setting of a total time oftwenty seconds has been selected at the same contrast setting of 60% `by the dial knob 62 which results in the green transmitting lter 50 being in the light beam for`40% ofthe total `exposure time or eight seconds after which the blue transmitting filter 49 is substituted, by operation of .the solenoid 54 in the manner previously described, for the remaining 60% of the total time, or twelve seconds, as shown by the full line in Fig. l0.

The modification shown in Figs. ll and l2 differs from that hereinbefore described only in the projector mechanism and the manner of producing the desired contrast .control for printing of a negative. In these latteriigures the projector comprises a housing carrying a pair of spotlights 102 and 103 angularly disposed relative-to each other so that their respective enclosed lamps 104 project a light beam which is reected downwardly through the condensers 105 by two reflecting plates 106 and 107 mounted on opposite sides of a supporting plate 108.

This supporting plate 108 is Isecured to a shaft 109 passing outwardly through a channel in the housing `and carrying a spur gear 110 on the outer end of such shaft.

,A torque type motor 112 is secured to the housing,

The lamps 104 are connected in parallel with each other and simply replace the lamp 38 in the circuit of Fig. 4

switch 83 to its Focus position, a green colored lightv beam is normally reflected downwardly through the condensers 105 since the reflector plate 106 is green.

After properly focusing the projector the operator moves switch 83 to its Print position which extinguishes the lamps 104 and then places the sensitized paper in position `as previously described. The timing and contrast dials 19 and 62, respectively are set as before mentioned and push-button 29 depressed to start the exposure. This again energizes the lamps 104 with the light therefrom striking green reflector plate 106 and passing downwardly through the condensers 105 to the paper 43 for the partial time period as set by the Contrast dial 62.

Upon expiration of this preset partial time of the complete exposure time, the tube 73 is rendered conductive as hereinbefore described which energizes motor 112 causing it to rotate the gears 114 and 110 together with shaft 109 and supporting plate 108. Rotation of this supporting plate 108 is limited to'l80 by a pin 115 which engages a xed stop 116 and hence such rotation removes reflector plate 106 from the position shown in Figs. ll

and 12 and substitutes the blue reflecting plate 107 there-v for during the remainder of the total time period. It will also be noted that while pin 115 is held against stop 116 the motor 112 remains energized, and hence is stalled during this period, but because it is of the torque type it is not overheated or otherwise damaged during this stalled condition.

When the total exposure time has elapsed arm 15 of the Timing potentiometer 25 will contact push-button 30 of microswitch 28 stopping the exposure at the preselected instant, as previously described, and a spiral spring 117, having one end anchored to the housing and its other endsecured to shaft 109, will cause opposite rotation of supporting plate 108 thus again reversing the reflecting plates 106 and 107 `and restoring them to their original position as shown in Figs. ll and l2.

From the foregoing it should thus be obvious to those skilled in the art that a timing device in form of a computing network has been herein provided which can be preset for any desired total range of time and during such total time period any desired percentage thereof can be accurately selected, wherein said percentage thereof will remain constant once selected and set, regardless of change in said total time period. Such timing device is thus operable to initiate a plurality of other operations at precise instants for a selected total time and for preselected percentages of such total time. Moreover, while the timing device of the present invention is adaptable to any usage where accurate timing is essential, such timing device is particularly desirable in connection with the making of photographic exposures to produce prints having correct contrast by causing the automatic introduction of the proper color-filters into the field of exposure at the right moment and for preselected periods of time.

Although several embodiments of the present invention have been shown and described it is to be understood that still further modiications thereof may be made without kdeparting from the spirit and scope of the appended claims.

I claim:

' 1. Apparatus for controlling exposure during the photographic printing of variable contrast photoiinishing paper comprising a light source, a color changing device having a plurality of movable differently colored filters operable to selectively position a different colored lter inthe path of the light beam from Asaid source during the exposure of the photonishing paper thereto, a timing 10 device having a total time control adapted to be preset to cause energization of said light source for any desired total time period, a contrast control forming a part ofsaid source and to substitute a filter of another color for the percentage of the total time period as selected by said contrast control, a circuit for supplying electrical energy to said color changing device to cause operation thereof including an electron discharge tube, and a control circuit including said total time control and said contrast control for normally impressing a negative biasing voltage on said electron discharge tube to render it non-conductive, and operable to vary the voltage impressed on said tube to render it conductive for closing said energy supply circuit for said color changing device during the percentage of the total time selected by said contrast control to retain the substituted color filter in the path of the light beam from said source during the remaining time period of energization of said light source by operation of said total time control, and while said Photofinishing paper is exposed to said energized light source.

2. Apparatus for controlling exposure during the pho tographic printing of variable contrast Photofinishingv paper comprising a light source, a color changing device having a plurality of movable differently colored filters operable to selectively position a different colored filter' in the path of the light beam from said source during the exposure of the photonishing paper thereto, a timing device having a total time control including a presettable potentiometer adapted to cause energization of said light source for any desired total time period as preset by` said potentiometer, a contrast control forming a part of said timing device and adapted to` be preset for any' desired percentage of the total time as selected by said timing control and operable to cause operation of said color changing ydevice at a precise instant to remove a lilter of one color from the path of the light beam from said source and to substitute a filter of another color for the percentage of the total time period as selected by said contrast control, a circuit for supplying electrical energy to said color changing device to cause operation thereof including an electron discharge tube, and a control circuit including the presettable potentiometer of said time control and said contrast control for normally impressing a negative biasing voltage on said electron discharge tube to render it non-conductive, and operable to vary the voltage impressed on said tube to render it conductive for closing said energy supply circuit for said color changing device during the percentage of the total time selected by said contrast control to retain the substituted color iilter in the path of the light beam from said source during the remaining time period of energization of said light source by operation of said total time control, and While said phototnishing paper is exposed to said energized light source.

3. Apparatus for controlling exposure during the photographic printing of variable contrast photofinishing paper comprising a light source, a color changing device having a plurality of movable diiterently colored lilters operable to selectively position a diiferent colored filter in the path of the light beam from said source during the exposure of the photofinishing paper thereto, a timing device having a total time control adapted to be preset to cause energization of said light source for any desired total time period, a contrast control forming a part of said timing device and including a presettable potentiometer adapted to be preset for any desired percentage of the total time as selected by said timing control and vice at a precise instant to remove a tilter of one color from. the path of the light beam from said sourceand tio: substitute a filter of another color for. the percentage ofthe total time period as selected by said potentiometer,l

a` circuit for supplying electrical energy to said' color changing device to cause operation thereof including an electron discharge tube, and a control circuit including said total time controly and the presettable potentiometer of said contrast control for normally impressingl a negative biasing voltage on said electron discharge tube. to-

p ath` Vof the light beam from said source during the remaining time period of energization of saidlight source by operation of said total time control, and While said Photofinishing paper is exposed'to said energized light source.

4. Apparatus for controlling exposure during the photographic printing of variable contrast photoiinishing papei-comprising a light source, a color changing device having a plurality of movable diiferently colored lters operable to selectively position a diiferent colored lter in the path of the light beam from said source during the exposure of the photolnishing paper thereto, a timing device having a total time control including a presettable potentiometer adapted to cause energization of said light source for any desired total time period as preset by said potentiometer, a contrast control forming a part of said timing device and 'also including a presettable'potenti ometer adapted to be preset for any desiredA percentage of the total time as selected by said timing control and operable to cause operation of said color changing device at a precise instant to remove a filter of one color from the path of the light beam from said source and to substitute `a ilter of another color for the percentage of the total time period as selected by the potentiometer of, said contrast control, a circuit for supplying electrical energy to said color changing device to cause operation thereof including an electron discharge tube, and a controlicircuit including the potentiometer of said total time controll and the potentiometer of said contrast control for normally impressing a negative biasing voltage on said electron discharge tube to render it non-conductive, and operable to vary the voltage impressed on said tube to render it conductive for closing said energy supply circuit for said color changing device during the percent-- ageofthetotal time selected by the potentiometer of said contrast control to retain the substituted color iilter in thek path of the light beam from saidsource'during the remaining time period of energization ofsaid light source by operation of the potentiometer of said total time control, and While said Photofinishing paper is exposed to said energized light source.

Apparatus for controlling exposure during the photographic printing of variable contrast photolinishing paper comprising a light source,` a color changing device having a plurality of movable differently'coloredL lters operable to selectively position a ditferent colored filter inthe path of the light beam from said source during the exposure of the photoiinishing paper thereto, a timing,

device having a total time control including a presettable and automatically varia-ble potentiometer operable to lcause energization of said light source for any desired vtotal time period as preset by said potentiometer, a contrast control forming a part of said timing device and also. including a presettable potentiometer adapted' to be preset for any desired percentage of the total time as selected by the potentiometer of said timing control and operable to cause operation of said color changingidevice at a precise instant to remove a ilter of one color from, the path of the light beam from said source and to 12 substitute a iilterof another color for the percentage of the total time period as selected by the potentiometer of said contrast control, an electric motor energizable by operation of said time control simultaneously with said light source and operable to cause the potentiometer of said time control to vary the voltage dropl thereacross, a circuit for supplying electrical energy to said color changing device to cause operation thereof including an electron discharge tube, and ya control circuit including the potentiometer of said total time control and the potentiometer of said contrast control for normally impressing a negative biasing voltage on said electron discharge tube to render it non-conductive, and operable to vary the voltage impressed on said tube in response to the variation in the voltage drop Iacross the potentiometer of said time control by operation of said motor to render saidy electron tube conductive for closing said energy supply vcircuit for said color changing device during the percentage of the total time selected by the potentiometer of said contrast control to retain the substituted color iilter in the path of the light beam from said source during the remaining time period o-f energization of said motor -and said light source by operation of said total time control, and while said photoiinishing paper is ex'- posed to said energized light source.

6. Apparatus for controlling exposure during the photographic printing of variable contrast photollinishing paper comprising a light source, a color changing device" including a movable member carrying a green transmitting iilter normally disposed in the path of the light beam from said source and a blue transmitting iilter substitutable for the green transmitting filter in the light beam from said source upon movement of said movable member and during the exposure of the photofinishing paper thereto, a timing device having a total time control including a two-arm potentiometer operable to cause energization of said light source for any desired total time period as preset by one of the arms of said potentiometer, a contrast control forming a part of said timing device and including a single-arm potentiometer adapted to be preset for any desired percentage of the total time as selected by the one arm of the potentiometer of said timing control, and operable to cause operation of the movable member of said color changing device at a precise instant to remove said green transmitting tilter from the path of the light beam from said source and to substitute said blue transmitting iilter for the percentage of the total time period as selected by the one ann o-f'the potentiometer of said time control; a constant-speed electric motor energizable by operation of said time control simultaneously With said light source and operable to cause movement of the other arm of the potentiometer of said time control to cause a variation in the voltage. drop yacross such potentiometer, a circuit for supplying electrical energy to said color changing device to cause operation thereof including an electron discharge tube, anda control circuit including the potentiometer of said total time control` and the potentiometer of said contrast control for normally impressing a negative biasing Voltage on saidl electron discharge tube to render it nonconductive, and operable to vary the voltage impressed on said tube in response to the variation in the voltage drop lacross the potentiometer of said time control upon movement of its other larm by said motor to render said electron discharge tube conductive for closing said energy supply circuit for said color changing device during the percentage of the total timeV selected bythe single arm of the potentiometer of said contract control to retain the blue transmitting iilter in the path of the light beam from said source for the remaining time period of energization of said motor iand said light source during themovement of the other arm of the potentiometer of said'total time control, and while said photofinishing paperis exposed to said energized-.light source,

7. Apparatus for controlling exposure during the printing of variable contrast photoiinishing paper comprising a source of light, a color changing device including a movable member carrying a green transmitting filter normally disposed in the light beam from said source and Ia blue transmitting filter substitutable for the green transmitting lilter in the light beam upon movement of said movable member, electrically operable means connected to said movable member and operable upon energization thereof to cause movement of said movable member with alternation ofsaid filters, a circuit for energizing said light source including a switch operable by an operator to close said circuit, a timing device having a time control including a two-arm potentiometer and operable upon the setting of one of said arms to control the total period of time of closure of said switch with attendant energization of said light source, a contrast control on said timing device including a single-arm potentiometer adapted to be preset for any desired percentage of the total time as selected by the one arm of the time control potentiometer, and operable to cause the energization of said electrically operable means with causation of attendant movement of said movable member and shifting of said filters at a precise instant and for the percentage of the total time as selected by the single arm of the contrast control potentiometer; ya constant-speed electric motor connected to the energizing circuit for said light source and energizable simultaneously with the latter by operation of said switch, and operable to move the other arm of the twoarm time control potentiometer and cause a variation in the voltage drop across such potentiometer, a circuit for supplying electrical energy to said electrically operable means including an electron discharge tube, and a control circuit including the two-arm time control potentiometer and the single-arm contrast potentiometer for normally impressing a negative bias on said electron discharge tube to render it non-conductive and thus maintaining the circuit to said electrically operable means in an open condition; and said control circuit being operable to vary the voltage impressed on said tube in response to the variation in the voltage drop across the time control potentiometer upon movement of its other arm by said motor, to render said electron discharge tube conductive and closing the circuit to said electrically operable means during the percentage of the total time selected by the singlearm of the contrast potentiometer, and until the circuit .to said light source and to said motor is interrupted by engagement of the other arm of said two-arm time control potentiometer with said switch at the end of travel of said arm, and while said photofnishing paper is exposed to said energized light source.

8. Apparatus for controlling exposure during the photographic printing of variable contrast photonshing paper comprising a base provided with a front panel, a time control potentiometer carried by said device having a pair of electrical contacts engageable with the turns of the ptentiometer winding and operable to preselect a voltage in an electrical circuit in which said potentiometer is included, a movable member on the front of said panel and operable to cause relative movement between one of said electrical contacts and the turns of said winding to select a voltage corresponding to a preselected total time period, a contrast potentiometer carried by said device and having an electrical contact engageable with the vturns of its winding and operable to preselect a voltage in an electrical circuit in which such contrast potentiometer is included, means operable by said contrast and time control potentiometers for actuating a photographic exposure control means, a movable member on the front of said panel and operable to move the contact of said contrast potentiometer to a point on its winding to select a voltage corresponding to a percentage of the total time as set by said time control potentiometer, a constamt-speed electric motor carried by said device and conthe winding thereof to cause a gradual variation in the voltage drop across said potentiometer when connected in an electric circuit, and a switch carried by said timing device for controlling operation of said motor and havlng a button depressible by an operator for closing said switch and starting said motor and having another butv ton engageable by the motor-driven electrical contact of said time control potentiometer at the end of its travel to open said switch and stop said motor.

9. Apparatus for controlling exposure during the photographic printing of variable contrast photonishing paper comprising a base provided with a front panel, a time control potentiometer carried by said device having a pair of electrical contacts engageable withthe turns of the potentiometer winding and operable to preselect a voltage in an electrical circuit in which such potentiometer is included, a movable member on the front of said panel and operable to cause relative movement between one of said electrical contacts and the turns of said winding to select a voltage corresponding to -a preselected total time period, a contrast potentiometer carried by said device and having an electrical contact engageable with the turns of its winding and operable to preselect a voltage in an electrical circuit in which such contrast potentiometer is included, means operable by said contrast and time control potentiometers for actuating a photographic exposure control means, a movable member on the front of said panel and operable to move the contact of said contrast potentiometer to a point on its winding to select a voltage corresponding to a percentage of the total time as set by said time control potentiometer, a constant-speed electric motor carried by said device and connected to the other electrical contact of said time control potentiometer for driving said contact over the turns of the winding thereof to cause a gradual variation in the voltage drop across said potentiometer when connected in an electric circuit, la switch carried by said timing device for controlling operation of said motor and having a button depressible by an operator for closing said switch and starting said motor and having another button engageable by the motor-driven electrical contact of said time control potentiometer at the end of its travel to open said switch and stop said motor, and potential energy storage means for automatically returning the motor-driven electrical contact of said time control potentiometer to its starting position upon stopping of said motor.

l0. Apparatus for controlling exposure during the photographic printing of variable contrast phototinishing paper comprising a base provided with a front panel, a time control potentiometer carried by said device having a toroidal winding disposed about the periphery of an insulating disc-like member, a stationary electrical contact engaging the turns of said winding at a point on its periphery and operable to preselect a voltage in an electrical circuit in which the toroidal winding of said time control potentiometer is included, a control knob on the front of said panel for rotating the toroidal winding of said time control potentiometer so as to position the engagement of said stationary electrical contact with a point on said winding to select a voltage corresponding to a preselected total time period, a contrast potentiometer carried by said device provided with a toroidal winding and having a rotatable electrical contact engageable with the turns of its toroidal winding and operable to preselect a voltage in an electrical circuit in which the toroidal Winding of said contrast potentiometer is included, means operable by said contrast and time control potentiometers for actuating a photographic exposure control means, a control knob on the front of said panel and operable to turn said rotatable contact to a point on said contrast potentiometer winding to select a voltage corresponding to a percentage of the total time as `set by said time con- 15 trol potentiometer, a rotatable electrical contact associated with the toroidal winding of said time control potentiometer, a constant-speed electric motor vcarried by said device and connected to the rotatable electrical contact of said time control potentiometer for rotating saidl contact over the turns of the toroidal winding to cause a gradual variation in the voltage drop across said potentiometer when connected in an electric circuit, "a switch carried by said timing device for controlling operation of said motor and having a button depressible by an operator for closing said switch and starting said motor and having another button engageable by the motor-driven rotatable electrical contact of said time control potentiometer at the end of its rotation corresponding to the lapse of the total preset time period :to open said switch and stop said motor, and a spiral spring associated with the motordriven rotatable electrical contact of said time control potentiometer to automatically return said rotatable contact to its starting position of engagement with the end turn of said toroidal winding upon stoppage of said motor.

References Cited in the le of this patent UNITED STATES PATENTS 2,430,253 Simmon Nov. 4, 1947 2,438,303 Simmon Mar. 23, 1948 2,463,985 Linde g Mar. 8, 1949 2,469,076 Rabinowitz May 3, 1949 2,518,947 Simmon Aug. 15, 1950 2,666,858 Levine Jan. 19, 1954 2,764,060 Horak Sept. 25, 1956 2,824,198 Bennett et al. Feb. 18, 1958 

